On the one hand, this invention relates to a method for manufacturing a toothed rack from an elastic material, the toothed rack being provided with teeth, and a toothed rack manufactured in accordance with this method on the other hand. Furthermore, this invention relates to a rapier rod profile for a rapier weaving machine provided with a toothed rack according to the invention.
In a rapier weaving machine, the rapiers are used to conduct weft yarns through the shed. Usually, two rapiers are operating, each coming from a different side of the weaving machine, in order to conduct the weft together through the shed. There are embodiments in existence where, from one side of the weaving machine, one rapier is conducting the weft yarn across the full width of the weaving machine. Each rapier here, is linked to the extremity of a rapier rod. In order to perform a reciprocating motion, the rapier rod is guided in a rapier guiding device and in order to drive the motion, it is comprising a toothed rack provided with teeth in mesh with a gear wheel, attached to a shaft installed in a horizontal or possibly a vertical position.
Since there is a tendency towards weaving machines operating at increasingly high speeds, also the speed at which the rapier rod is moving through the shed is increasing. Moreover, the rapier has to pick up or to drop the weft yarn at one end of the motion, and to transmit or to take over the weft yarn at the other end of its motion. During this take over the rapier will come to a halt each time to resume its full speed in the other direction.
The shock loads occurring during this reversal of the motion are considerable and are strongly increasing at increasing operational speeds or at increasing width of the weaving machine and also at increasing weight of the moving portion, more particularly the weight of the rapier and the rapier rod. These shock loads are transmitted by the driving gearwheel to the teeth of the rapier rod, because of which the toothed rack part of the rapier rod is subjected to a heavy strain.
The toothed rack should have both elastic properties to absorb the shock load and at the same time, the whole, including the rapier rod profile, should be sufficiently strong and stiff to resist the effect of the forces occurring.
For the absorbing effect, the toothed rack is therefore made of an elastic material. In order to be able to resist the effect of the forces occurring, the toothed rack is fixed in a strong and stiff rapier rod. Since the effect of the forces occurring is essentially of a dynamic nature, this means that when mass of the whole moving along (rapier rod with toothed rack in combination with the rapier) may be removed while the remaining stiffness will be sufficient, this will offer the essential advantage of being able to weave at a higher speed.
According to the state-of-the-art, many attempts have been made to reduce the weight of the moving portion, more particularly by making use of other materials: therefore, in the publication of the German patent DE-PS 3527202, the rapier rod is made with an integrated toothed rack profile of a synthetic material, reinforced with carbon fibres in order to reduce the effect of the dynamic forces occurring without using great masses.
The reinforced synthetic material is machined layer after layer, the layers being stacked one on top of the other, pressed together and cured to become a whole. This method is an expensive and labour-intensive operation, the accuracy of form of the teeth being difficult to realize by this stacking method. Moreover, in each layer, fibres are cut through near the tooth profile. This will give cause to premature wear, the more as these fibres cut through are situated in the area where the load is most heavy.
The publication of the German patent DE 3638673 shows an embodiment of the rapier rod, where the toothed rack is made of elastic synthetic material, which, in the most heavy loaded area right below the surface of the tooth from top to root, is reinforced by means of carbon fibres, following the profile of the tooth. The cost here, will be reduced by using the expensive carbon fibres only locally, but the production method remains difficult, time-consuming and delicate.
The publication of the European patent EP 394639 a separate toothed rack being glued to a rapier rod profile is again aimed at. The toothed part is made of carbon fibre reinforced synthetic material, the fibres following the teeth and not being cut through. The teeth being hollow here, which means that when gluing the toothed rack to the rapier rod profile only the root of the tooth will become attached. This embodiment is still expensive to produce, and gluing the toothed rack onto the rapier rod profile remains a delicate operation, as the glued joint has to be capable of absorbing considerable forces. Moreover, with such an embodiment, gluing remains limited to relatively small surfaces at the root of the tooth.
In the publication of the German patent DE 19608254, a tooth profile, as described in EP 394639 is integrated into a rapier rod to form a whole. This will be a favourable, as the weight of the rapier rod is concerned, however, it still remains a delicate en complicated operation in order to obtain the final result desired.
Because of what has been said above, for practical uses, toothed racks made of an elastic synthetic material attached to carbon fibre reinforced rapier rod profiles are still used today.